Personally, I would say, do NOT give up on cloud management. Here is why I say that...I know you might be frustrated now, but I can tell you, back in 2019/2020 time, when S1C was so new, I must have spent over 100 hours on so many issues with it with same guy in TAC, we were like best friends : -). Anyway, on a more serious note, when I compare it to those days, its like night and day.
Put it this way...say, for example you have onprem management and someone makes a mistake pushing policy remotely and its 4-5 hours away drive (as an example). I dont know anyone who would be willing to spend that much time driving late at night to fix an issue. With S1C, thats never a challenge, as even if that happened, you can log into it from any computer in the world with Internet access, revert change, all good.
Now, onto your original issue...I second what @Chris_Atkinson said. Some things to check:
-test incognito browser window (I find google chrome works best)
-from settings in main portal, you can try restart the instance
-if both fail to fix the problem and other browsers have same issue, please contact TAC, ask them if they can install recommended jumbo take and also log into backend (please provide tenant identifier), so they could verify further
I have access to 8 clients who use smart cloud management, so Im very familiar with it.
Happy to do remote if you allow that and we can check together.
Hope that helps.
Best,
Andy